1. Field of the Invention
The present invention relates generally to a method and apparatus for ordering retransmissions in a Multi-Input Multi-Output (MIMO) system using N transmission antennas and M reception antennas (N×M Antennas), and in particular, to a method and apparatus for ordering retransmissions each antenna by utilizing Alamouti space-time coding instead of multiplying a unitary matrix when the next packet is retransmitted, for a preprocessing process, in a MIMO system using N×M antennas (hereinafter referred to as an “N×M MIMO system”).
2. Description of the Related Art
The MIMO system using multiple transmission/reception antennas, which is a wireless transmission scheme capable of maximizing a diversity gain and a data rate through multiplexing, will serve as the core technology of the next generation mobile communication system. Automatic Repeat reQuest (ARQ) protocol is error control means for overcoming packet transmission errors frequently occurring in a poor wireless channel.
In addition, Hybrid Automatic Repeat reQuest (HARQ) protocol is being adopted in the standard as a scheme for maximizing retransmissions. The HARQ protocol is a combination of Forward Error Correction (FEC) and ARQ scheme. According to the HARQ protocol, a receiver attempts error correction through FEC, and attempts retransmission if the receiver fails in the error correction. In order to adaptively cope with an instantaneous change in a channel state, the receiver can transmit additional parity information or merge additional parity bits with repeatedly received data information instead of changing a coding rate at every retransmission, to gradually improve error correction capability.
A system using the combined HARQ and MIMO (hereinafter referred to as a “MIMO HARQ system”) depends on a variation of interference signal amplitude of combined signal of a receiver based on the selection of retransmission ordering each antenna, greatly affecting its HARQ performance. Therefore, there is a need for a method capable of optimizing selection of retransmission ordering.